Find that quite hard to believe as a student who lives in ACT after growing up in KL and has travelled to Melbourne and Sydney, and even Perth, Brisbane, and Gold Coast years ago.
Of course I don't live in Sydney so I might not have the full picture but feel free to elaborate.
When we talk about costs like these (and ignore FX rates) we also need to account for relative salary. It's much higher in Australia. In KL a grad might get 3,000 monthly if lucky (plenty of evidence on this forum that many get below that even in what's seen as high performing industries, and Jobstreet will confirm this), which translates to 36,000 pa. Let's ignore SOCSO, EPF, and taxes for now. A Sydney or Melbourne grad can easily get 60,000 pa, sometimes 80,000 pa. We're talking service industry and not working in mines or oil fields. You may want to account for maybe 25% taxes since the starting taxes for income above AUD 18k is around 17-20% if I remember correctly. Even then it's 45,000 to 60,000.
Now I can observe (anecdotal, not fact or statistics) there are plenty of things that cost the same nominal units of money in either country. A restaurant meal (MYR 30 or AUD 30). A suit jacket. A house or apartment unit (~500k).
Now the Australian salary starts at a much higher base. Assuming equal growth, equal performance, comparable economic conditions blah blah the Australian is gonna have a much higher pay in several years' time. Who is better off?
$7 sounds cheap for fast food. Is that location highly accessible, or is that price point common, or is the portion big enough, i.e. will many people be able to enjoy $7 meals too?
$20 for a proper shirt sounds like it's been discounted quite a bit and in KL you can also get 3-shirt or 2-shirt specials all year round for quite cheap, quality stuff. Where do you shop in Malaysia? We have some of the cheapest goods around the region and it attracts so many people from Hong Kong, Singapore, Australia and New Zealand.
too long to elaborate and this is a much more complex issue than simply comparing how much fast food costs even when you match dollar for dollar etc - what we look at is purchasing power over essential items and even people who dedicate careers to doing this like economists, professors and all those overpaid people in the banks etc cant come to an agreement.
what is more important, and should be more important, is intangible and "soft" differences, like quality of life, safety, freedom (political freedom, etc). Southern neighbour singapore is known to be expensive, why do so many people still migrate there instead of KL?